For numerous applications such as contact lenses, catheters, peristaltic pump chambers, condoms, implant materials, arteriovenous shunts, gastroenteric feed tubes and endotracheal tubes it is desired to have a material such as a polyurethane, acrylic polyester, or a vinyl resin or a rubber having a much lower coefficient of friction when wet than is possible with those materials per se. In the prior art polyvinylpyrollidone has been chemically grafted to a polymer substrate by first activating the substrate by irradiation or chemically. The resultant coating does not have a very low coefficient of friction. Polyurethane coatings are well known, but do not have a very low coefficient of friction. Heretofore, polymer substrates have been given a lower coefficient of friction by coating them with a non-permanent coating such as silicone or given a fluorocarbon coating neither of which is hydrophilic and which do not have as low a coefficient of friction as desired. Also fluorocarbon coatings are hard to handle because they have a low coefficient of friction at all times.
These problems have been solved surprisingly by this invention by providing a coating of polyvinylpyrollidone-polyurethane interpolymer. The hydrophilic coatings of this invention are advantageous since they have a very low coefficient of friction when wetted with a water base liquid or a lower aliphatic alcohol such as methanol or ethanol and yet are much less slippery when dry. This is an advantage, for example, in the handling of catheters since it is desirable to have them not slippery for handling but protecting the patient by becoming slippery when contacting an aqueous fluid. This is an important advantage of the invention in view of the high degree of lubricity of the coatings. Further, the coating thickness is not limited to a few molecular monolayers as in the case of other methods such as chemical or radiation grafting and may be applied in thicknesses of several hundred micrometers. In addition the coatings are non-reactive with respect to living tissue and are non-thrombogenic when in contact with blood. For each of these reasons, the product and method of the invention are unique and of great value.